University of Cambridge > > Climate and Environmental Dynamics - Department of Geography > Quantifying transport time and degradation of terrigenous organic carbon across the East Siberian Arctic shelf

Quantifying transport time and degradation of terrigenous organic carbon across the East Siberian Arctic shelf

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Climate Environmental Dynamics Research Group Seminar

Permafrost soils in the Arctic store large quantities of organic matter, roughly twice the amount of carbon that was present in the atmosphere before the industrial revolution. This freeze-locked carbon pool is susceptible to thawing caused by amplified global warming at high latitudes. The remobilization of old permafrost carbon facilitates its degradation to carbon dioxide and methane, thereby providing a positive feedback to climate change.

Accelerating coastal erosion in addition to projected rising river discharge with enhancing sediment loads are anticipated to transport increasing amounts of land-derived organic carbon (OC) to the Arctic Ocean. On its shallow continental shelves, this material may be remineralized in the water column or in the sediments, transported without being altered off shelf towards the deep sea of the Arctic Interior or buried in marine sediments and hence sequestered from the contemporary carbon cycle. The fate of terrigenous material in the marine environment, though offering potentially important mechanisms to either strengthen or attenuate the permafrost-carbon climate feedback, is so far insufficiently understood.

We have used sediments from the wide East Siberian Arctic Shelf, the world’s largest shelf-sea system, to investigate some of the key processes for OC cycling. A range of bulk sediment properties, carbon isotopes and molecular markers were employed to elucidate the relative importance of different organic matter sources, the role of cross-shelf transport and the relevance of degradation during transport and after burial.

This talk focuses on how we can employ compound-specific radiocarbon analyses of terrestrial biomarkers to determine cross-shelf transport times and quantify degradation rates for terrigenous OC (terrOC). For the 600 km from the Lena River Delta to the Laptev Sea shelf edge our quantitative estimate resulted in 3600 ± 300 years. During transport, terrOC was reduced by ~85%, thus yielding a degradation rate constant of 2.4 ± 0.6 kyr-1. Hence, terrOC degradation during cross-shelf transport constitutes a carbon source to the atmosphere over millennial time. For the contemporary carbon cycle on the other hand, slow terrOC degradation brings considerable attenuation of the decadal-centennial permafrost carbon-climate feedback caused by global warming.

This talk is part of the Climate and Environmental Dynamics - Department of Geography series.

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